German chemist Otto Diels studied under Emil Fischer, and improved techniques for the synthesis of organic chemical compounds. In 1906 he discovered a new oxide of carbon, carbon suboxide (C3O2), and in 1922 he developed a new method for dehydrogenating compounds. In work that greatly improved the scientific understanding of cholesterol and other steroids, he dehydrogenated cholesterol to produce 'Diels hydrocarbon' (C18H16) in 1927. The following year, Diels and his student Kurt Alder described how an alkene reacts with a diene to create a cyclohexene. Now called the Diels-Alder reaction, this allowed the development and mass production of affordable synthetic alkaloids, insecticides, plastics, polymers, rubber, and steroids. For this, Diels and Alder shared the Nobel Prize for Chemistry in 1950.

He also developed the first practical method using metallic selenium to remove hydrogen atoms from certain organic molecules. After his home and laboratory in Kiel were destroyed by Allied bombing in 1944, Diels ceased his research and filed retirement papers, but he continued teaching part-time at the University of Kiel until 1950. Though his work was of major consequence to 20th century science and industry, Diels is unfairly almost unknown beyond his native Germany, and his biography remains unwritten beyond a few retrospective articles in scientific journals. His father, Hermann Alexander Diels, was a well-known historian and theologist, and his brother, Ludwig Diels, became a prominent botanist of his era.